Sewage testing helps guide Qld’s coronavirus pandemic response

It’s the canary in the coalmine of coronavirus detection and, as Queensland health authorities work to hunt down every possible case of the pandemic virus, this vital analysis is being used to alert them to potential infections they may have missed.

It’s the canary in the coalmine of coronavirus detection – sewage testing.

As Queensland health authorities work to hunt down every possible case of the pandemic virus, wastewater analysis is being used to alert them to potential infections they may have missed.

Although the state recorded another day without any cases on Thursday, evidence of SARS-CoV-2, the virus that causes COVID-19, has been picked up in ‘low levels” in Queensland sewage for the third time in a month.

Four weeks after the virus was first detected in sewage in the Cannonvale-Airlie Beach area, wastewater analysis has found more viral particles there, prompting renewed calls for Queenslanders to remain vigilant about getting tested if unwell.

Sewage testing is of most benefit in regions that have not previously had a case, or have gone long periods of time since their last infection, as is the situation in the Whitsundays.

Pop-up fever clinics can then be deployed, as they have in Airlie Beach, aimed at finding early cases in a cluster before the virus has a chance to spread through the community.

The Whitsundays region has recorded six cases of the COVID-19 virus, five of them overseas acquired, but one that could not be traced back to a known contact.

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Queensland Chief Health Officer Dr Jeannette Young. Photo: Annette Dew

With asymptomatic infections making up about 20 per cent of cases, the concern is for silent outbreaks to be occurring that could quickly turn into a second wave in Queensland.

Sewage surveillance is not new – it has been used globally to detect previously unknown cases of poliovirus and by Australian researchers to monitor illicit drug consumption.

Health experts both in Australia and overseas have added it to their arsenal of technology to provide an early warning system of SARS-CoV-2 cases – just like canaries were once used to detect the presence of explosive gases in coal mines.

“We’re doing more and more here in Queensland and NSW has been doing it and that gives us a heads up,” Chief Health Officer Jeannette Young said, ahead of the border zone being extended between the two states.

“We can’t test everyone in the community but we can test the sewage, which then gives us an idea of what’s going on in that community and it tells us that there is virus or there isn’t virus. We’re just using the technology that’s at our disposal.”

NSW Health publishes the results of its sewage testing weekly. Queensland used those results to assist in its decision to widen the border zone further into northern NSW.

Queensland wastewater testing for the pandemic virus is part of a pilot project launched in July.

University of Queensland virologist Ian Mackay said scientists were still learning about the benefits and limitations of sewage analysis.

“These are still methods that are being evaluated and their usefulness examined,” Associate Professor Mackay said.

“It has exciting potential, but its best use is likely to be for finding hints that virus is in an area where no human cases have been seen for weeks or longer.

“When we already know cases are present, we won’t learn much that’s new if we find a wastewater positive result in the same area.”

UQ environmental health scientist Kevin Thomas, who is involved in the project said the sewage testing picked up genetic fragments of the virus.

Professor Thomas said the wastewater analysis, which also picked up evidence of the virus in Hervey Bay sewage last month, was unable to say whether the person shedding the virus was still infectious.

Dr Young has speculated the latest positive sewage result in Airlie Beach may be someone who continues to shed dead virus, but is no longer contagious.

“We know that you shed virus for a long, long time and that can be intermittent, so the best thing here is for people who live in that area to come forward and get tested,” she said.

Queensland is testing sewage for SARS-CoV-2 in Brisbane, Ipswich, Logan, Gold Coast, Sunshine Coast, Hervey Bay, Mackay, Cannonvale-Airlie Beach, Townsville, Cairns, Warwick, Stanthorpe and Bundaberg.

While wastewater analysis is providing valuable information about the possibility of cases in those areas, it will never replace the benefit of Queenslanders getting tested when they develop symptoms.

“Although we’re doing a lot of sewage testing, which is helping enormously, we still can’t be totally confident that we might not have a case somewhere in the state that we’re not aware of at this point in time,” Dr Young said.

“This is why I really need people who have symptoms to come forward and get tested. You then need to isolate yourself until you get that result.”